Field of the Invention: This invention relates to water-soluble polylactones and water-soluble reaction products of polylactones with organic polyisocyanates. In another aspect, this invention relates to coating compositions prepared from such water-soluble materials.
Brief Description of the Prior Art: U.S. Pat. No. 3,169,945 to Hostettler et al discloses polylactones which are formed from ring opening a lactone such as epsilon-caprolactone with an active hydrogen-containing material. Examples of suitable active hydrogen-containing materials are polyols,, amino alcohols, monohydroxy carboxylic acids and monoamino carboxylic acids, as well as polyester polyols. The polylactones are reacted with polyisocyanates to form highly crosslinked polyurethanes which have the consistency of millible gums. These products are principally of interest as rubber substitutes.
Japanese Pat. No. 72.35077 discloses polymerizing epsilon-caprolactone with compounds of the formula ##STR1## where R is alkyl, cycloalkyl or aryl, A and B are the same or different divalent aliphatic radicals and HX is hydrochloric, sulphuric, nitric or phosphoric. The polylactone can be used as an intermediate or polyurethane formation.
It is well known in the art that polylactones, such as those prepared from ring opening epsilon-caprolactone with polyols such as ethylene glycol and trimethylolpropane, can be co-reacted with polyol-containing carboxylic acids, such as dimethylolpropionic acid and organic polyisocyanates. The unreacted carboxylic acid groups can be neutralized to make the polymer water dispersible and useful in aqueous coating compositions.
Unfortunately, there are certain disadvantages in preparing polyurethane with polyol-containing carboxylic acids such as dimethylolpropionic acid. These polyols, in addition to other polyols normally used, require more organic polyisocyanate to react with the polyol-carboxylic acid. In forming light stable compositions requiring aliphatic or cycloaliphatic diisocyanates, this can become prohibitively expensive. In addition, dimethylolpropionic acid and similar materials are crystalline and have a low rate of dissolution making formulation difficult.
According to the present invention, a polyol-containing carboxylic acid such as dimethylolpropionic acid is pre-reacted with a lactone such as epsilon-caprolactone to form a polylactone polyol containing free carboxylic acid groups. The polylactone can then be reacted with organic polyisocyanates to form polyurethanes containing free carboxylic acid groups which can be neutralized and dispersed in aqueous medium. The present invention overcomes many of the disadvantages of the prior art in that it is easier to use less polyisocyanate to get the same relative amount of carboxylic acid group into the polymer. By pre-reacting the dimethylolpropionic acid with epsilon-caprolactone, a non-crystalline adduct is produced making polyurethane formulation easier than with crystalline dimethylolpropionic acid.
As mentioned above, it has also been found that polyurethanes prepared by reacting organic polyisocyanates with the adduct of dimethylolpropionic acid and epsilon-caprolactone are more water dispersible and deposit as coatings with greater adhesion to the substrate and less water sensitivity than comparable polyurethanes prepared by reacting organic polyisocyanates with dimethylolpropionic acid and conventional polylactone diols by a one-shot technique.